GB1282572A - Apparatus for processing echo sounder signals - Google Patents

Abstract

1282572 Fishing sonar WHITE FISH AUTHORITY 27 Jan 1970 [29 Oct 1968] 51276/68 Heading H4D [Also in Division G4] For determining the probable rate of catch of fish by a fishing vessel, the number of echoes received in each sounding by an echo sounder from fish in a predetermined depth band is normalized (to compensate for the increasing width of the sounding beam with depth) to obtain a respective quantity corresponding to the number of echoes which would be received if the same fish were a standard depth below the echo sounder, respective estimates of the number of fish caught are derived from these quantities in accordance with a predetermined relationship between the estimate and the said quantity, the estimates are summed over a given time interval, the sum is indicated as an estimated catch rate, and provision is made for up-dating the predetermined relationship. In the embodiment shown on echo sounder receiver channel is provided with time-variedgain (to compensate for sound attenuation with depth) and optional A.G.C. The sea-bed echo and fish echoes are then distinguished by means of amplitude gates 18, 42 and an echo slope gate 44. Gate 25 is opened by a transmitted sound pulse and closed by the resulting sea-bed echo to feed clock pulses to counter 33 giving a digital depth measurement for display at 35 and for normalization purposes. A blanking pulse generator 30 prevents premature closure of the gate 25 by a fish echo. Shift register 49 is arranged to count those fish echoes from a 4 feet high band adjacent the sea-bed (when bottomtrawling), and this count is transferred to a register 54. Normalization is effected at 60, where register 54 count is divided by the square of the depth. In a given fishing operation, the normalized counts are summed on accumulator 76 then divided into the actual catch value of a previous fishing operation to obtain at 82 a factor RA. An assumed correction factor RF is multiplied at 66 by each normalized count to give estimated catch counts which are summed at 71 over two-minute periods to give estimated catch rate values for display at 73 and analogue recording at 75. The estimated catch counts are also summed at 68 over the whole fishing operation to give a total catch display at 70. For the next fishing operation the correction factor RF is updated by allotting the factor RA a weight α at 83, multiplying the old RF factor by 1-α, and summing at 84 product (1-α) x RF with the weighted factor αRA to give a new RF value. In a modification for midwater fishing, shift register 49 and depth counter 33 are not used and instead a manually-controlled time gate feeds fish echoes from a selected depth band to register 54.